Shift register circuit

ABSTRACT

A shift register circuit with waveform-shaping function includes plural shift register stages. Each shift register stage includes a first input unit, a pull-up unit, a pull-down circuit, a second input unit, a control unit and a waveform-shaping unit. The first input unit is utilized for outputting a first driving control voltage in response to a first gate signal. The pull-up unit pulls up a second gate signal in response to the first driving control voltage. The pull-down circuit is employed to pull down the first driving control voltage and the second gate signal. The second input unit is utilized for outputting a second driving control voltage in response to the first gate signal. The control unit provides a control signal in response to the second driving control voltage and an auxiliary signal. The waveform-shaping unit performs a waveform-shaping operation on the second gate signal in response to the control signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shift register circuit, and moreparticularly, to a shift register circuit with waveform shapingfunction.

2. Description of the Prior Art

Along with the advantages of thin appearance, low power consumption, andlow radiation, liquid crystal displays (LCDs) have been widely appliedin various electronic products for panel displaying. The operation of aliquid crystal display is featured by varying voltage drops betweenopposite sides of a liquid crystal layer for twisting the angles of theliquid crystal molecules in the liquid crystal layer so that thetransmittance of the liquid crystal layer can be controlled forillustrating images with the aid of light source provided by a backlightmodule. In general, the liquid crystal display comprises plural pixelunits, a source driver, and a shift register circuit. The source driveris utilized for providing plural data signals to be written into thepixel units. The shift register circuit comprises a plurality of shiftregister stages which are employed to generate plural gate signals forcontrolling the operations of writing the data signals into the pixelunits. That is, the shift register circuit is a crucial device forproviding a control of writing the data signals into the pixel units.

FIG. 1 is a schematic diagram showing a prior-art shift registercircuit. As shown in FIG. 1, the shift register circuit 100 comprises aplurality of shift register stages and, for ease of explanation,illustrates an (N−1)th shift register stage 111, an Nth shift registerstage 112 and an (N+1)th shift register stage 113. Each shift registerstage is employed to generate one corresponding gate signal furnished toone corresponding gate line based on a first clock CK1 and a secondclock CK2 having a phase opposite to the first clock CK1. For instance,the (N−1)th shift register stage 111 is employed to generate a gatesignal SGn−1 furnished to a gate line GLn−1, the Nth shift registerstage 112 is employed to generate a gate signal SGn furnished to a gateline GLn, and the (N+1)th shift register stage 113 is employed togenerate a gate signal SGn+1 furnished to a gate line GLn+1. The Nthshift register stage 112 comprises a pull-up unit 120, an input unit130, an energy-store unit 125, a discharging unit 140, a pull-down unit150 and a control unit 160. The pull-up unit 120 pulls up the gatesignal SGn in response to a driving control voltage VQn. The dischargingunit 140 and the pull-down unit 150 are employed to pull down thedriving control voltage VQn and the gate signal SGn respectively inresponse to a pull-down control signal generated by the control unit160.

In the operation of the shift register circuit 100, the shift registerstages provide the gate signals having periodical pulses to the pixelunits for writing the data signals to become plural pixel voltages.However, each pulse of the gate signals is analogous to an ideal squarewaveform, and the falling edge of each pulse may cause an occurrence ofpulling down the written pixel voltages due to the coupling effect ofthe parasitic capacitors corresponding to the pixel units, whichphenomenon is referred to as the feed-through effect. The feed-througheffect is likely to incur image flicker, and the display quality ofliquid crystal displays using the shift register circuit 100 istherefore degraded.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a shiftregister circuit with waveform shaping function is set forth forproviding plural gate signals to plural gate lines. The shift registercircuit comprises a plurality of shift register stages. And an Nth shiftregister stage of the shift register stages comprises a first inputunit, a pull-up unit, a pull-down circuit, a second input unit, acontrol unit, a waveform-shaping unit, and a pull-down unit. The firstinput unit, electrically connected to an (N−1)th shift register stage ofthe shift register stages for receiving an (N−1)th gate signal of thegate signals, is utilized for outputting a first driving control voltagein response to the (N−1)th gate signal. The pull-up unit, electricallyconnected to the first input unit and an Nth gate line of the gatelines, is utilized for pulling up an Nth gate signal of the gate signalsin response to the first driving control voltage and a system clock. TheNth gate line is employed to deliver the Nth gate signal. The pull-downcircuit, electrically connected to the first input unit and the pull-upunit, is employed to pull down the first driving control voltage and theNth gate signal. The second input unit, electrically connected to the(N−1)th shift register stage for receiving the (N−1)th gate signal, isutilized for outputting a second driving control voltage in response tothe (N−1)th gate signal. The control unit, electrically connected to thesecond input unit, is utilized for generating a control signal inresponse to the second driving control voltage and an auxiliary signal.The waveform-shaping unit, electrically connected to the control unitand the Nth gate line, is utilized for performing a waveform-shapingoperation on the Nth gate signal in response to the control signal. Thepull-down unit, electrically connected to an (N+1)th shift registerstage of the shift register stages for receiving an (N+1)th gate signalof the gate signals, is utilized for pulling down the second drivingcontrol voltage in response to the (N+1)th gate signal.

In accordance with another embodiment of the present invention, a shiftregister circuit with waveform shaping function is set forth forproviding plural gate signals to plural gate lines. The shift registercircuit comprises a plurality of shift register stages. And an Nth shiftregister stage of the shift register stages comprises an input unit, apull-up unit, a pull-down circuit, a control unit, and awaveform-shaping unit. The input unit, electrically connected to an(N−1)th shift register stage of the shift register stages for receivingan (N−1)th gate signal of the gate signals, is utilized for outputting adriving control voltage in response to the (N−1)th gate signal. Thepull-up unit, electrically connected to the input unit and an Nth gateline of the gate lines, is utilized for pulling up an Nth gate signal ofthe gate signals in response to the driving control voltage and a systemclock. The Nth gate line is employed to deliver the Nth gate signal. Thepull-down circuit, electrically connected to the input unit and thepull-up unit, is employed to pull down the driving control voltage andthe Nth gate signal. The control unit, electrically connected to theinput unit, is utilized for generating a control signal in response tothe driving control voltage and an auxiliary signal. Thewaveform-shaping unit, electrically connected to the control unit andthe Nth gate line, is utilized for performing a waveform-shapingoperation on the Nth gate signal in response to the control signal.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a prior-art shift registercircuit.

FIG. 2 is a schematic diagram showing a shift register circuit inaccordance with a first embodiment of the present invention.

FIG. 3 is a schematic diagram showing related signal waveforms regardingthe operation of the shift register circuit in FIG. 2, having time alongthe abscissa.

FIG. 4 is a schematic diagram showing a shift register circuit inaccordance with a second embodiment of the present invention.

FIG. 5 is a schematic diagram showing a shift register circuit inaccordance with a third embodiment of the present invention.

FIG. 6 is a schematic diagram showing related signal waveforms regardingthe operation of the shift register circuit in FIG. 5, having time alongthe abscissa.

FIG. 7 is a schematic diagram showing a shift register circuit inaccordance with a fourth embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Here,it is to be noted that the present invention is not limited thereto.

FIG. 2 is a schematic diagram showing a shift register circuit inaccordance with a first embodiment of the present invention. As shown inFIG. 2, the shift register circuit 200 comprises a plurality of shiftregister stages and, for ease of explanation, illustrates an (N−1)thshift register stage 211, an Nth shift register stage 212 and an (N+1)thshift register stage 213. For the sake of brevity, only the internalstructure of the Nth shift register stage 212 is exemplified in detail.The other shift register stages are similar to the Nth shift registerstage 212 and can be inferred by analogy. In the operation of the shiftregister circuit 200, the (N−1)th shift register stage 211 is employedto generate a gate signal SGn−1 furnished to a gate line GLn−1, the Nthshift register stage 212 is employed to generate a gate signal SGnfurnished to a gate line GLn, and the (N+1)th shift register stage 213is employed to generate a gate signal SGn+1 furnished to a gate lineGLn+1.

The Nth shift register stage 212 comprises a pull-up unit 220, a firstinput unit 230, an energy-store unit 225, a pull-down circuit 240, asecond input unit 280, a first control unit 285, a first pull-down unit290 and a waveform-shaping unit 295. The first input unit 230,electrically connected to the (N−1)th shift register stage 211, isutilized for outputting a first driving control voltage VQn1 in responseto the gate signal SGn−1. That is, the gate signal SGn−1 also functionsas a start pulse signal for enabling the Nth shift register stage 212.The energy-store unit 225, electrically connected to the first inputunit 230 and the pull-up unit 220, functions to store the first drivingcontrol voltage VQn1. The pull-up unit 220, electrically connected tothe first input unit 230 and the gate line GLn, is put in use forpulling up the gate signal SGn of the gate line GLn in response to thefirst driving control voltage VQn1 and a first clock CK1. The pull-downcircuit 240 comprises a second control unit 245, a second pull-down unit255 and a third pull-down unit 250. The second control unit 245,electrically connected to the first input unit 230, is utilized forgenerating a second control signal Sc2 in response to the first drivingcontrol voltage VQn1 and a second clock CK2 having a phase opposite tothe first clock CK1. The second pull-down unit 255, electricallyconnected to the second control unit 245 and the gate line GLn, isutilized for pulling down the gate signal SGn in response to the secondcontrol signal Sc2. The third pull-down unit 250, electrically connectedto the second control unit 245 and the first input unit 230, is utilizedfor pulling down the first driving control voltage VQn1 in response tothe second control signal Sc2.

The second input unit 280, electrically connected to the (N−1)th shiftregister stage 211, is utilized for outputting a second driving controlvoltage VQn2 in response to the gate signal SGn−1. The first controlunit 285, electrically connected to the second input unit 280, isutilized for generating a first control signal Sc1 in response to thesecond driving control voltage VQn2 and an auxiliary signal Saux. Thefirst pull-down unit 290, electrically connected to the (N+1)th shiftregister stage 213 and the second input unit 280, is utilized forpulling down the second driving control voltage VQn2 in response to thegate signal SGn+1. The waveform-shaping unit 295, electrically connectedto the first control unit 285 and the gate line GLn, is utilized forperforming a waveform-shaping operation on the gate signal SGn inresponse to the first control signal Sc1.

In the embodiment shown in FIG. 2, the pull-up unit 220 comprises afirst transistor 221, the first input unit 230 comprises a secondtransistor 231, the energy-store unit 225 comprises a capacitor 226, thesecond input unit 280 comprises a third transistor 281, the firstcontrol unit 285 comprises a fourth transistor 286, the first pull-downunit 290 comprises a fifth transistor 291, the waveform-shaping unit 295comprises a sixth transistor 296, the second pull-down unit 255comprises a seventh transistor 256, the third pull-down unit 250comprises an eighth transistor 251, and the second control unit 245comprises a ninth transistor 246 and a tenth transistor 247. The firsttransistor 221 through the tenth transistor 247 are thin filmtransistors or field effect transistors.

The first transistor 221 comprises a first end for receiving the firstclock CK1, a second end electrically connected to the gate line GLn, anda gate end electrically connected to the first input unit 230. Thecapacitor 226 is electrically connected between the gate and second endsof the first transistor 221. The second transistor 231 comprises a firstend electrically connected to the (N−1)th shift register stage 211 forreceiving the gate signal SGn−1, a gate end electrically connected tothe first end, and a second end electrically connected to the gate endof the first transistor 221. The third transistor 281 comprises a firstend electrically connected to the (N−1)th shift register stage 211 forreceiving the gate signal SGn−1, a gate end electrically connected tothe first end, and a second end electrically connected to the firstcontrol unit 285. The fourth transistor 286 comprises a first end forreceiving the auxiliary signal Saux, a second end electrically connectedto the waveform-shaping unit 295, and a gate end electrically connectedto the second end of the third transistor 281. The fifth transistor 291comprises a first end electrically connected to the second end of thethird transistor 281, a second end for receiving a low power voltageVss, and a gate end electrically connected to the (N+1)th shift registerstage 213 for receiving the gate signal SGn+1. The sixth transistor 296comprises a first end electrically connected to the gate line GLn, asecond end for receiving the low power voltage Vss, and a gate endelectrically connected to the second end of the fourth transistor 286.

The seventh transistor 256 comprises a first end electrically connectedto the gate line GLn, a gate end electrically connected to the secondcontrol unit 245 for receiving the second control signal Sc2, and asecond end for receiving the low power voltage Vss. The eighthtransistor 251 comprises a first end electrically connected to thesecond end of the second transistor 231, a gate end electricallyconnected to the second control unit 245 for receiving the secondcontrol signal Sc2, and a second end for receiving the low power voltageVss. The ninth transistor 246 comprises a first end for receiving thesecond clock CK2, a gate end electrically connected to the first end,and a second end electrically connected to both the gate ends of theseventh transistor 256 and the eighth transistor 251. The tenthtransistor 247 comprises a first end electrically connected to thesecond end of the ninth transistor 246, a gate end electricallyconnected to the second end of the second transistor 231, and a secondend for receiving the low power voltage Vss.

FIG. 3 is a schematic diagram showing related signal waveforms regardingthe operation of the shift register circuit 200 in FIG. 2, having timealong the abscissa. The signal waveforms in FIG. 3, from top to bottom,are the auxiliary signal Saux, the first clock CK1, the second clockCK2, the gate signal SGn−1, the first driving control voltage VQn1, thesecond driving control voltage VQn2, the first control signal Sc1, thegate signal SGn and the gate signal SGn+1. As shown in FIG. 3, during aninterval T1, the gate signal SGn−1 is switching from low-level voltageto high-level voltage, and the second transistor 231 and the thirdtransistor 281 are then turned on. Accordingly, both the first drivingcontrol voltage VQn1 and the second driving control voltage VQn2 areshifting up to a first high voltage Vh1 for turning on the firsttransistor 221 and the fourth transistor 286 respectively. Meanwhile,the capacitor 226 is utilized for storing the first driving controlvoltage VQn1, and the first driving control voltage VQn1 is furtheremployed to turn on the tenth transistor 247 for pulling down the secondcontrol signal Sc2 to the low power voltage Vss so as to turn off boththe seventh transistor 256 and the eighth transistor 251.

During an interval T2, the gate signal SGn−1 is switching fromhigh-level voltage to low-level voltage, and the second transistor 231and the third transistor 281 are then turned off. Accordingly, both thefirst driving control voltage VQn1 and the second driving controlvoltage VQn2 become floating voltages. Concurrently, along with theswitching of the first clock CK1 from low-level voltage to high-levelvoltage, the first driving control voltage VQn1 is further boosted fromthe first high voltage Vh1 to a second high voltage Vh2 due to acapacitive coupling effect caused by the device capacitor of the firsttransistor 221. Accordingly, the first transistor 221 is continuouslyturned on and the gate signal SGn is then pulled up from low-levelvoltage to a third high voltage Vh3.

During an interval T3, the auxiliary signal Saux is switching fromlow-level voltage to high-level voltage, and therefore the seconddriving control voltage VQn2 is further boosted from the first highvoltage Vh1 to a fourth high voltage Vh4 due to a capacitive couplingeffect caused by the device capacitor of the fourth transistor 286.Accordingly, the fourth transistor 286 is continuously turned on and thefirst control signal Sc1 is then pulled up from low-level voltage tohigh-level voltage. Meanwhile, the first control signal Sc1 withhigh-level voltage turns on the sixth transistor 296 and, in turn, thegate signal SGn is decreasing from the third high voltage Vh3 to a fifthhigh voltage Vh5 during the interval T3.

During an interval T4, the first clock CK1 is switching from high-levelvoltage to low-level voltage, and therefore the gate signal SGn isshifting from the fifth high voltage Vh5 to low-level voltage. Also, thefirst driving control voltage VQn1 is pulled down to low-level voltagedue to a coupling effect of the capacitor 226. And the tenth transistor247 is therefore turned off. In the meantime, since the second controlsignal Sc2 is shifting up to high-level voltage following a change ofthe second clock CK2 from low-level voltage to high-level voltage, theseventh transistor 256 and the eighth transistor 251 are then turned onfor pulling down the gate signal SGn and the first driving controlvoltage VQn1 to low-level voltage. Besides, by making use of the gatesignal SGn as a start pulse signal, the (N+1)th shift register stage 213is enabled to generate the gate signal SGn+1 having high-level voltageduring the interval T4, and therefore the fifth transistor 291 is turnedon for pulling down the second driving control voltage VQn2 from thefourth high voltage Vh4 to the low power voltage Vss during the intervalT4. It is noted that the falling edge of the gate signal SGn is shiftingfrom the fifth high voltage Vh5 down to low-level voltage, instead ofshifting from the third high voltage Vh3 down to low-level voltage, andtherefore the voltage difference of the falling edge can besignificantly reduced for mitigating the feed-through effect. For thatreason, the display quality of liquid crystal displays using the shiftregister circuit 200 can be enhanced following a reduction of imageflicker.

FIG. 4 is a schematic diagram showing a shift register circuit inaccordance with a second embodiment of the present invention. As shownin FIG. 4, the shift register circuit 400 comprises a plurality of shiftregister stages and, for ease of explanation, illustrates an (N−1)thshift register stage 411, an Nth shift register stage 412 and an (N+1)thshift register stage 413. For the sake of brevity, only the internalstructure of the Nth shift register stage 412 is exemplified in detail.The other shift register stages are similar to the Nth shift registerstage 412 and can be inferred by analogy. The circuit structure of theNth shift register stage 412 is similar to that of the Nth shiftregister stage 212 shown in FIG. 2, differing in that the pull-downcircuit 240 is replaced with the pull-down circuit 440. The pull-downcircuit 440 comprises a second control unit 445, a second pull-down unit455, a third pull-down unit 450 and a fourth pull-down unit 460. Thesecond control unit 445, electrically connected to the first input unit230, is utilized for generating a second control signal Sc2 in responseto the first driving control voltage VQn1 and the second clock CK2. Thesecond pull-down unit 455, electrically connected to the second controlunit 445 and the gate line GLn, is utilized for pulling down the gatesignal SGn in response to the second control signal Sc2. The thirdpull-down unit 450, electrically connected to the second control unit445 and the first input unit 230, is utilized for pulling down the firstdriving control voltage VQn1 in response to the second control signalSc2. The fourth pull-down unit 460, electrically connected to the(N+1)th shift register stage 413 and the gate line GLn, is utilized forpulling down the gate signal SGn in response to the gate signal SGn+1.

In the embodiment shown in FIG. 4, the second pull-down unit 455comprises a seventh transistor 456, the third pull-down unit 450comprises an eighth transistor 451, the second control unit 445comprises a ninth transistor 446, a tenth transistor 447, an eleventhtransistor 448 and a twelfth transistor 449, and the fourth pull-downunit 460 comprises a thirteenth transistor 461. The seventh transistor456 through the thirteenth transistor 461 are thin film transistors orfield effect transistors. The seventh transistor 456 comprises a firstend electrically connected to the gate line GLn, a gate end electricallyconnected to the second control unit 445 for receiving the secondcontrol signal Sc2, and a second end for receiving the low power voltageVss. The eighth transistor 451 comprises a first end electricallyconnected to the second end of the second transistor 231, a gate endelectrically connected to the second control unit 445 for receiving thesecond control signal Sc2, and a second end for receiving the low powervoltage Vss.

The ninth transistor 446 comprises a first end for receiving the secondclock CK2, a second end electrically connected to both the gate ends ofthe seventh transistor 456 and the eighth transistor 451, and a gate endelectrically connected to the eleventh transistor 448. The tenthtransistor 447 comprises a first end electrically connected to thesecond end of the ninth transistor 446, a gate end electricallyconnected to the second end of the second transistor 231, and a secondend for receiving the low power voltage Vss. The eleventh transistor 448comprises a first end for receiving the second clock CK2, a gate endelectrically connected to the first end, and a second end electricallyconnected to the gate end of the ninth transistor 446. The twelfthtransistor 449 comprises a first end electrically connected to thesecond end of the eleventh transistor 448, a gate end electricallyconnected to the second end of the second transistor 231, and a secondend for receiving the low power voltage Vss. The thirteenth transistor461 comprises a first end electrically connected to the gate line GLn, agate end electrically connected to the (N+1)th shift register stage 413for receiving the gate signal SGn+1, and a second end for receiving thelow power voltage Vss.

The signal waveforms regarding the operation of the shift registercircuit 400 are substantially identical to the signal waveforms shown inFIG. 3. In the operation of the shift register circuit 400, during theinterval T4, the thirteenth transistor 461 is capable of pulling downthe gate signal SGn in response to the gate signal SGn+1. That is, boththe seventh transistor 456 and the thirteenth transistor 461 areemployed to pull down the gate signal SGn. The internal structure of thesecond control unit 445 is well known to those skilled in the art and,for the sake of brevity, further similar discussion thereof is omitted.

FIG. 5 is a schematic diagram showing a shift register circuit inaccordance with a third embodiment of the present invention. As shown inFIG. 5, the shift register circuit 500 comprises a plurality of shiftregister stages and, for ease of explanation, illustrates an (N−1)thshift register stage 511, an Nth shift register stage 512 and an (N+1)thshift register stage 513. For the sake of brevity, only the internalstructure of the Nth shift register stage 512 is exemplified in detail.The other shift register stages are similar to the Nth shift registerstage 512 and can be inferred by analogy. In the operation of the shiftregister circuit 500, the (N−1)th shift register stage 511 is employedto generate a gate signal SGn−1 furnished to a gate line GLn−1, the Nthshift register stage 512 is employed to generate a gate signal SGnfurnished to a gate line GLn, and the (N+1)th shift register stage 513is employed to generate a gate signal SGn+1 furnished to a gate lineGLn+1.

The Nth shift register stage 512 comprises a pull-up unit 520, an inputunit 530, an energy-store unit 525, a pull-down circuit 540, a firstcontrol unit 585 and a waveform-shaping unit 595. The input unit 530,electrically connected to the (N−1)th shift register stage 511, isutilized for outputting a driving control voltage VQn in response to thegate signal SGn−1. That is, the gate signal SGn−1 also functions as astart pulse signal for enabling the Nth shift register stage 512. Theenergy-store unit 525, electrically connected to the input unit 530 andthe pull-up unit 520, functions to store the driving control voltageVQn. The pull-up unit 520, electrically connected to the input unit 530and the gate line GLn, is put in use for pulling up the gate signal SGnof the gate line GLn in response to the driving control voltage VQn anda first clock CK1.

The pull-down circuit 540 comprises a second control unit 545, a firstpull-down unit 555 and a second pull-down unit 550. The second controlunit 545, electrically connected to the input unit 530, is utilized forgenerating a second control signal Sc2 in response to the drivingcontrol voltage VQn and a second clock CK2 having a phase opposite tothe first clock CK1. The first pull-down unit 555, electricallyconnected to the second control unit 545 and the gate line GLn, isutilized for pulling down the gate signal SGn in response to the secondcontrol signal Sc2. The second pull-down unit 550, electricallyconnected to the second control unit 545 and the input unit 530, isutilized for pulling down the driving control voltage VQn in response tothe second control signal Sc2. The first control unit 585, electricallyconnected to the input unit 530, is utilized for generating a firstcontrol signal Sc1 in response to the driving control voltage VQn and anauxiliary signal Saux. The waveform-shaping unit 595, electricallyconnected to the first control unit 585 and the gate line GLn, isutilized for performing a waveform-shaping operation on the gate signalSGn in response to the first control signal Sc1.

In the embodiment shown in FIG. 5, the pull-up unit 520 comprises afirst transistor 521, the input unit 530 comprises a second transistor531, the energy-store unit 525 comprises a capacitor 526, the firstcontrol unit 585 comprises a third transistor 586, the waveform-shapingunit 595 comprises a fourth transistor 596, the first pull-down unit 555comprises a fifth transistor 556, the second pull-down unit 550comprises a sixth transistor 551, and the second control unit 545comprises a seventh transistor 546 and an eighth transistor 547. Thefirst transistor 521 through the eighth transistor 547 are thin filmtransistors or field effect transistors.

The first transistor 521 comprises a first end for receiving the firstclock CK1, a second end electrically connected to the gate line GLn, anda gate end electrically connected to the input unit 530. The capacitor526 is electrically connected between the gate and second ends of thefirst transistor 521. The second transistor 531 comprises a first endelectrically connected to the (N−1)th shift register stage 511 forreceiving the gate signal SGn−1, a gate end electrically connected tothe first end, and a second end electrically connected to the gate endof the first transistor 521. The third transistor 586 comprises a firstend for receiving the auxiliary signal Saux, a second end electricallyconnected to the waveform-shaping unit 595, and a gate end electricallyconnected to the second end of the second transistor 531. The fourthtransistor 596 comprises a first end electrically connected to the gateline GLn, a second end for receiving the low power voltage Vss, and agate end electrically connected to the second end of the thirdtransistor 586.

The fifth transistor 556 comprises a first end electrically connected tothe gate line GLn, a gate end electrically connected to the secondcontrol unit 545 for receiving the second control signal Sc2, and asecond end for receiving the low power voltage Vss. The sixth transistor551 comprises a first end electrically connected to the second end ofthe second transistor 531, a gate end electrically connected to thesecond control unit 545 for receiving the second control signal Sc2, anda second end for receiving the low power voltage Vss. The seventhtransistor 546 comprises a first end for receiving the second clock CK2,a gate end electrically connected to the first end, and a second endelectrically connected to both the gate ends of the fifth transistor 556and the sixth transistor 551. The eighth transistor 547 comprises afirst end electrically connected to the second end of the seventhtransistor 546, a gate end electrically connected to the second end ofthe second transistor 531, and a second end for receiving the low powervoltage Vss.

FIG. 6 is a schematic diagram showing related signal waveforms regardingthe operation of the shift register circuit 500 in FIG. 5, having timealong the abscissa. The signal waveforms in FIG. 6, from top to bottom,are the auxiliary signal Saux, the first clock CK1, the second clockCK2, the gate signal SGn−1, the driving control voltage VQn, the firstcontrol signal Sc1, the gate signal SGn and the gate signal SGn+1. Asshown in FIG. 6, during an interval T1, the gate signal SGn−1 isswitching from low-level voltage to high-level voltage, and the secondtransistor 531 is then turned on. Accordingly, the driving controlvoltage VQn is shifting up to a first high voltage Vh1 for turning onthe first transistor 521 and the third transistor 586. Meanwhile, thecapacitor 526 is utilized for storing the driving control voltage VQn,and the driving control voltage VQn is further employed to turn on theeighth transistor 547 for pulling down the second control signal Sc2 tothe low power voltage Vss so as to turn off both the fifth transistor556 and the sixth transistor 551.

During an interval T2, the gate signal SGn−1 is switching fromhigh-level voltage to low-level voltage, and the second transistor 531is then turned off. Accordingly, the driving control voltage VQn becomesa floating voltage. Concurrently, along with the switching of the firstclock CK1 from low-level voltage to high-level voltage, the drivingcontrol voltage VQn is further boosted from the first high voltage Vh1to a second high voltage Vh2 due to a capacitive coupling effect causedby the device capacitor of the first transistor 521. Accordingly, thefirst transistor 521 and the third transistor 586 are continuouslyturned on, and the gate signal SGn is then pulled up from low-levelvoltage to a third high voltage Vh3.

During an interval T3, the auxiliary signal Saux is switching fromlow-level voltage to high-level voltage, and therefore the drivingcontrol voltage VQn is further boosted from the second high voltage Vh2to a fourth high voltage Vh4 due to a capacitive coupling effect causedby the device capacitor of the third transistor 586. Accordingly, thefirst transistor 521 and the third transistor 586 are continuouslyturned on, and the first control signal Sc1 is then pulled up fromlow-level voltage to high-level voltage. It is noted that the size ofthe device capacitor of the third transistor 586 has an effect on thevoltage difference between the fourth high voltage Vh4 and the secondhigh voltage Vh2. In the meantime, the first control signal Sc1 withhigh-level voltage turns on the fourth transistor 596 and, in turn, thegate signal SGn is decreasing from the third high voltage Vh3 to a fifthhigh voltage Vh5 during the interval T3.

During an interval T4, the first clock CK1 is switching from high-levelvoltage to low-level voltage, and therefore the gate signal SGn isshifting from the fifth high voltage Vh5 to low-level voltage. Also, thedriving control voltage VQn is pulled down to low-level voltage due to acoupling effect of the capacitor 526. And the eighth transistor 547 istherefore turned off. In the meantime, since the second control signalSc2 is shifting up to high-level voltage following a change of thesecond clock CK2 from low-level voltage to high-level voltage, the fifthtransistor 556 and the sixth transistor 551 are then turned on forpulling down the gate signal SGn and the driving control voltage VQn tolow-level voltage. Besides, by making use of the gate signal SGn as astart pulse signal, the (N+1)th shift register stage 513 is enabled togenerate the gate signal SGn+1 having high-level voltage during theinterval T4. Similarly, the falling edge of the gate signal SGn isshifting from the fifth high voltage Vh5 down to low-level voltage,instead of shifting from the third high voltage Vh3 down to low-levelvoltage, and therefore the voltage difference of the falling edge can besignificantly reduced for mitigating the feed-through effect. For thatreason, the display quality of liquid crystal displays using the shiftregister circuit 500 can be enhanced following a reduction of imageflicker.

FIG. 7 is a schematic diagram showing a shift register circuit inaccordance with a fourth embodiment of the present invention. As shownin FIG. 7, the shift register circuit 700 comprises a plurality of shiftregister stages and, for ease of explanation, illustrates an (N−1)thshift register stage 711, an Nth shift register stage 712 and an (N+1)thshift register stage 713. For the sake of brevity, only the internalstructure of the Nth shift register stage 712 is exemplified in detail.The other shift register stages are similar to the Nth shift registerstage 712 and can be inferred by analogy. The circuit structure of theNth shift register stage 712 is similar to that of the Nth shiftregister stage 512 shown in FIG. 5, differing in that the pull-downcircuit 540 is replaced with the pull-down circuit 740. The pull-downcircuit 740 comprises a second control unit 745, a first pull-down unit755, a second pull-down unit 750 and a third pull-down unit 760. Thesecond control unit 745, electrically connected to the input unit 530,is utilized for generating a second control signal Sc2 in response tothe driving control voltage VQn and the second clock CK2. The firstpull-down unit 755, electrically connected to the second control unit745 and the gate line GLn, is utilized for pulling down the gate signalSGn in response to the second control signal Sc2. The second pull-downunit 750, electrically connected to the second control unit 745 and theinput unit 530, is utilized for pulling down the driving control voltageVQn in response to the second control signal Sc2. The third pull-downunit 760, electrically connected to the (N+1)th shift register stage 713and the gate line GLn, is utilized for pulling down the gate signal SGnin response to the gate signal SGn+1.

In the embodiment shown in FIG. 7, the first pull-down unit 755comprises a fifth transistor 756, the second pull-down unit 750comprises a sixth transistor 751, the second control unit 745 comprisesa seventh transistor 746, an eighth transistor 747, a ninth transistor748 and a tenth transistor 749, and the third pull-down unit 760comprises an eleventh transistor 761. The fifth transistor 756 throughthe eleventh transistor 761 are thin film transistors or field effecttransistors. The fifth transistor 756 comprises a first end electricallyconnected to the gate line GLn, a gate end electrically connected to thesecond control unit 745 for receiving the second control signal Sc2, anda second end for receiving the low power voltage Vss. The sixthtransistor 751 comprises a first end electrically connected to thesecond end of the second transistor 531, a gate end electricallyconnected to the second control unit 745 for receiving the secondcontrol signal Sc2, and a second end for receiving the low power voltageVss.

The seventh transistor 746 comprises a first end for receiving thesecond clock CK2, a second end electrically connected to both the gateends of the fifth transistor 756 and the sixth transistor 751, and agate end electrically connected to the ninth transistor 748. The eighthtransistor 747 comprises a first end electrically connected to thesecond end of the seventh transistor 746, a gate end electricallyconnected to the second end of the second transistor 531, and a secondend for receiving the low power voltage Vss. The ninth transistor 748comprises a first end for receiving the second clock CK2, a gate endelectrically connected to the first end, and a second end electricallyconnected to the gate end of the seventh transistor 746. The tenthtransistor 749 comprises a first end electrically connected to thesecond end of the ninth transistor 748, a gate end electricallyconnected to the second end of the second transistor 531, and a secondend for receiving the low power voltage Vss. The eleventh transistor 761comprises a first end electrically connected to the gate line GLn, agate end electrically connected to the (N+1)th shift register stage 713for receiving the gate signal SGn+1, and a second end for receiving thelow power voltage Vss.

The signal waveforms regarding the operation of the shift registercircuit 700 are substantially identical to the signal waveforms shown inFIG. 6. In the operation of the shift register circuit 700, during theinterval T4, the eleventh transistor 761 is capable of pulling down thegate signal SGn in response to the gate signal SGn+1. That is, both thefifth transistor 756 and the eleventh transistor 761 are employed topull down the gate signal SGn. The internal structure of the secondcontrol unit 745 is well known to those skilled in the art and, for thesake of brevity, further similar discussion thereof is omitted.

In conclusion, compared with the prior-art shift register circuit, theshift register circuit of the present invention provides the gatesignals having smaller voltage difference of falling edges formitigating the feed-through effect. For that reason, the display qualityof liquid crystal displays using the shift register circuit of thepresent invention can be enhanced following a reduction of imageflicker. Besides, regarding the structure of the shift register circuitof the present invention, the pull-down circuit is not limited to theaforementioned embodiments, and any other circuit capable of pullingdown the driving control voltage and the gate signal can be employed toreplace the pull-down circuits illustrated in the aforementionedembodiments without having any substantial effect on thewaveform-shaping function of the shift register circuit of the presentinvention.

The present invention is by no means limited to the embodiments asdescribed above by referring to the accompanying drawings, which may bemodified and altered in a variety of different ways without departingfrom the scope of the present invention. Thus, it should be understoodby those skilled in the art that various modifications, combinations,sub-combinations and alternations might occur depending on designrequirements and other factors insofar as they are within the scope ofthe appended claims or the equivalents thereof.

1. A shift register circuit for providing plural gate signals to pluralgate lines, the shift register circuit comprising a plurality of shiftregister stages, an Nth shift register stage of the shift registerstages comprising: a first input unit, electrically connected to an(N−1)th shift register stage of the shift register stages for receivingan (N−1)th gate signal of the gate signals, for outputting a firstdriving control voltage in response to the (N−1)th gate signal; apull-up unit, electrically connected to the first input unit and an Nthgate line of the gate lines, for pulling up an Nth gate signal of thegate signals in response to the first driving control voltage and afirst clock, wherein the Nth gate line is employed to deliver the Nthgate signal; a pull-down circuit, electrically connected to the firstinput unit and the pull-up unit, for pulling down the first drivingcontrol voltage and the Nth gate signal; a second input unit,electrically connected to the (N−1)th shift register stage for receivingthe (N−1)th gate signal, for outputting a second driving control voltagein response to the (N−1)th gate signal; a first control unit,electrically connected to the second input unit, for generating a firstcontrol signal in response to the second driving control voltage and anauxiliary signal; a waveform-shaping unit, electrically connected to thefirst control unit and the Nth gate line, for performing awaveform-shaping operation on the Nth gate signal in response to thefirst control signal; and a first pull-down unit, electrically connectedto an (N+1)th shift register stage of the shift register stages forreceiving an (N+1)th gate signal of the gate signals, for pulling downthe second driving control voltage in response to the (N+1)th gatesignal.
 2. The shift register circuit of claim 1, wherein the Nth shiftregister stage further comprises: a capacitor, electrically connectedbetween the first input unit and the Nth gate line, for storing thefirst driving control voltage.
 3. The shift register circuit of claim 1,wherein the first input unit comprises a transistor, the transistorcomprising: a first end, electrically connected to the (N−1)th shiftregister stage, for receiving the (N−1)th gate signal; a gate endelectrically connected to the first end of the transistor; and a secondend electrically connected to the pull-up unit and the pull-downcircuit.
 4. The shift register circuit of claim 1, wherein the pull-upunit comprises a transistor, the transistor comprising: a first end forreceiving the first clock; a gate end, electrically connected to thefirst input unit, for receiving the first driving control voltage; and asecond end electrically connected to the Nth gate line.
 5. The shiftregister circuit of claim 1, wherein the second input unit comprises atransistor, the transistor comprising: a first end, electricallyconnected to the (N−1)th shift register stage, for receiving the (N−1)thgate signal; a gate end electrically connected to the first end of thetransistor; and a second end electrically connected to the first controlunit and the first pull-down unit.
 6. The shift register circuit ofclaim 1, wherein the first control unit comprises a transistor, thetransistor comprising: a first end for receiving the auxiliary signal; agate end, electrically connected to the second input unit, for receivingthe second driving control voltage; and a second end electricallyconnected to the waveform-shaping unit.
 7. The shift register circuit ofclaim 1, wherein the first pull-down unit comprises a transistor, thetransistor comprising: a first end electrically connected to the secondinput unit; a gate end, electrically connected to the (N+1)th shiftregister stage, for receiving the (N+1)th gate signal; and a second endfor receiving a low power voltage.
 8. The shift register circuit ofclaim 1, wherein the waveform-shaping unit comprises a transistor, thetransistor comprising: a first end electrically connected to the Nthgate line; a gate end, electrically connected to the first control unit,for receiving the first control signal; and a second end for receiving alow power voltage.
 9. The shift register circuit of claim 1, wherein thepull-down circuit comprises: a second control unit, electricallyconnected to the first input unit, for generating a second controlsignal in response to the first driving control voltage and a secondclock having a phase opposite to the first clock; a second pull-downunit, electrically connected to the second control unit and the Nth gateline, for pulling down the Nth gate signal in response to the secondcontrol signal; and a third pull-down unit, electrically connected tothe second control unit and the first input unit, for pulling down thefirst driving control voltage in response to the second control signal.10. The shift register circuit of claim 9, wherein: the second controlunit comprises: a first transistor comprising a first end for receivingthe second clock, a gate end electrically connected to the first end ofthe first transistor, and a second end electrically connected to boththe second pull-down unit and the third pull-down unit; and a secondtransistor comprising a first end electrically connected to the secondend of the first transistor, a gate end electrically connected to thefirst input unit for receiving the first driving control voltage, and asecond end for receiving a low power voltage; the second pull-down unitcomprises: a third transistor comprising a first end electricallyconnected to the Nth gate line, a gate end electrically connected to thesecond end of the first transistor for receiving the second controlsignal, and a second end for receiving the low power voltage; and thethird pull-down unit comprises: a fourth transistor comprising a firstend electrically connected to the first input unit, a gate endelectrically connected to the second end of the first transistor forreceiving the second control signal, and a second end for receiving thelow power voltage.
 11. The shift register circuit of claim 9, whereinthe pull-down circuit further comprises: a fourth pull-down unit,electrically connected to the Nth gate line and the (N+1)th shiftregister stage, for pulling down the Nth gate signal in response to the(N+1)th gate signal.
 12. The shift register circuit of claim 11,wherein: the second control unit comprises: a first transistorcomprising a first end for receiving the second clock, a second endelectrically connected to both the second pull-down unit and the thirdpull-down unit, and a gate end; a second transistor comprising a firstend electrically connected to the second end of the first transistor, agate end electrically connected to the first input unit for receivingthe first driving control voltage, and a second end for receiving a lowpower voltage; a third transistor comprising a first end for receivingthe second clock, a gate end electrically connected to the first end ofthe third transistor, and a second end electrically connected to thegate end of the first transistor; and a fourth transistor comprising afirst end electrically connected to the second end of the thirdtransistor, a gate end electrically connected to the first input unitfor receiving the first driving control voltage, and a second end forreceiving the low power voltage; the second pull-down unit comprises: afifth transistor comprising a first end electrically connected to theNth gate line, a gate end electrically connected to the second end ofthe first transistor for receiving the second control signal, and asecond end for receiving the low power voltage; the third pull-down unitcomprises: a sixth transistor comprising a first end electricallyconnected to the first input unit, a gate end electrically connected tothe second end of the first transistor for receiving the second controlsignal, and a second end for receiving the low power voltage; and thefourth pull-down unit comprises: a seventh transistor comprising a firstend electrically connected to the Nth gate line, a gate end electricallyconnected to the (N+1)th shift register stage for receiving the (N+1)thgate signal, and a second end for receiving the low power voltage.
 13. Ashift register circuit for providing plural gate signals to plural gatelines, the shift register circuit comprising a plurality of shiftregister stages, an Nth shift register stage of the shift registerstages comprising: an input unit, electrically connected to an (N−1)thshift register stage of the shift register stages for receiving an(N−1)th gate signal of the gate signals, for outputting a drivingcontrol voltage in response to the (N−1)th gate signal; a pull-up unit,electrically connected to the input unit and an Nth gate line of thegate lines, for pulling up an Nth gate signal of the gate signals inresponse to the driving control voltage and a first clock, wherein theNth gate line is employed to deliver the Nth gate signal; a pull-downcircuit, electrically connected to the input unit and the pull-up unit,for pulling down the driving control voltage and the Nth gate signal; afirst control unit, electrically connected to the input unit, forgenerating a first control signal in response to the driving controlvoltage and an auxiliary signal, the auxiliary signal being a pulsesignal; and a waveform-shaping unit, electrically connected to the firstcontrol unit and the Nth gate line, for performing a waveform-shapingoperation on the Nth gate signal in response to the first controlsignal.
 14. The shift register circuit of claim 13, wherein the Nthshift register stage further comprises: a capacitor, electricallyconnected between the input unit and the Nth gate line, for storing thedriving control voltage.
 15. The shift register circuit of claim 13,wherein the input unit comprises a transistor, the transistorcomprising: a first end, electrically connected to the (N−1)th shiftregister stage, for receiving the (N−1)th gate signal; a gate endelectrically connected to the first end of the transistor; and a secondend electrically connected to the pull-up unit, the pull-down circuitand the first control unit.
 16. The shift register circuit of claim 13,wherein the pull-up unit comprises a transistor, the transistorcomprising: a first end for receiving the first clock; a gate end,electrically connected to the input unit, for receiving the drivingcontrol voltage; and a second end electrically connected to the Nth gateline.
 17. The shift register circuit of claim 13, wherein the firstcontrol unit comprises a transistor, the transistor comprising: a firstend for receiving the auxiliary signal; a gate end, electricallyconnected to the input unit, for receiving the driving control voltage;and a second end electrically connected to the waveform-shaping unit.18. The shift register circuit of claim 13, wherein the waveform-shapingunit comprises a transistor, the transistor comprising: a first endelectrically connected to the Nth gate line; a gate end, electricallyconnected to the first control unit, for receiving the first controlsignal; and a second end for receiving a low power voltage.
 19. Theshift register circuit of claim 13, wherein the pull-down circuitcomprises: a second control unit, electrically connected to the inputunit, for generating a second control signal in response to the drivingcontrol voltage and a second clock having a phase opposite to the firstclock; a first pull-down unit, electrically connected to the secondcontrol unit and the Nth gate line, for pulling down the Nth gate signalin response to the second control signal; and a second pull-down unit,electrically connected to the second control unit and the input unit,for pulling down the driving control voltage in response to the secondcontrol signal.
 20. The shift register circuit of claim 19, wherein: thesecond control unit comprises: a first transistor comprising a first endfor receiving the second clock, a gate end electrically connected to thefirst end of the first transistor, and a second end electricallyconnected to both the first pull-down unit and the second pull-downunit; and a second transistor comprising a first end electricallyconnected to the second end of the first transistor, a gate endelectrically connected to the input unit for receiving the drivingcontrol voltage, and a second end for receiving a low power voltage; thefirst pull-down unit comprises: a third transistor comprising a firstend electrically connected to the Nth gate line, a gate end electricallyconnected to the second end of the first transistor for receiving thesecond control signal, and a second end for receiving the low powervoltage; and the second pull-down unit comprises: a fourth transistorcomprising a first end electrically connected to the input unit, a gateend electrically connected to the second end of the first transistor forreceiving the second control signal, and a second end for receiving thelow power voltage.
 21. The shift register circuit of claim 19, whereinthe pull-down circuit further comprises: a third pull-down unit,electrically connected to an (N+1)th shift register stage of the shiftregister stages for receiving an (N+1)th gate signal of the gatesignals, for pulling down the Nth gate signal in response to the (N+1)thgate signal.
 22. The shift register circuit of claim 21, wherein: thesecond control unit comprises: a first transistor comprising a first endfor receiving the second clock, a second end electrically connected toboth the first pull-down unit and the second pull-down unit, and a gateend; a second transistor comprising a first end electrically connectedto the second end of the first transistor, a gate end electricallyconnected to the input unit for receiving the driving control voltage,and a second end for receiving a low power voltage; a third transistorcomprising a first end for receiving the second clock, a gate endelectrically connected to the first end of the third transistor, and asecond end electrically connected to the gate end of the firsttransistor; and a fourth transistor comprising a first end electricallyconnected to the second end of the third transistor, a gate endelectrically connected to the input unit for receiving the drivingcontrol voltage, and a second end for receiving the low power voltage;the first pull-down unit comprises: a fifth transistor comprising afirst end electrically connected to the Nth gate line, a gate endelectrically connected to the second end of the first transistor forreceiving the second control signal, and a second end for receiving thelow power voltage; the second pull-down unit comprises: a sixthtransistor comprising a first end electrically connected to the inputunit, a gate end electrically connected to the second end of the firsttransistor for receiving the second control signal, and a second end forreceiving the low power voltage; and the third pull-down unit comprises:a seventh transistor comprising a first end electrically connected tothe Nth gate line, a gate end electrically connected to the (N+1)thshift register stage for receiving the (N+1)th gate signal, and a secondend for receiving the low power voltage.